AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Invited Paper SS1-MoM3
Adsorption Dynamics and Desorption Kinetics of Argon and Methane on MgO(100)

Monday, November 3, 2003, 9:00 am, Room 326

Session: Gas-Surface Dynamics
Presenter: B.D. Kay, Pacific Northwest National Laboratory
Authors: B.D. Kay, Pacific Northwest National Laboratory
Z. Dohnalek, Pacific Northwest National Laboratory
G.K. Schenter, Pacific Northwest National Laboratory
L.R. Corrales, Pacific Northwest National Laboratory
R.S. Smith, Pacific Northwest National Laboratory
Correspondent: Click to Email
The adsorption dynamics and desorption kinetics of Ar and CH4 on MgO(100) are studied using a combination of molecular beam scattering and temperature programmed desorption (TPD). Both Ar and CH4 exhibit an initial trapping probability that decreases dram atically with increasing kinetic energy and is independent of incident angle indicating adsorption is a barrier-less process obeying total energy scaling. The trapping probability for both adsorbates increases roughly linearly with the increasing coverag e in the first layer. Such behavior can be described by a simple model involving constant but different trapping probabilities on clean and adsorbate covered MgO(100) with fast intra-layer diffusion leading to preferential filling of the bare MgO(100). An a logous behavior is observed for trapping on the second and third layers and indicates layer-by-layer growth of the adsorbate overlayer with layer dependent trapping probabilities. Analysis of the TPD spectra yields desorption energies of 8.5 and 13 kJ/m ol e for Ar and CH4, respectively in agreement with previous measurements and theoretical calculations. The total energy scaling observed for the initial trapping of Ar and CH4 on MgO(100) is in sharp contrast with the normal energy scaling previously obs erv ed for these species on Pt(111). These differences indicate that the adsorbate-substrate interaction is laterally smooth on Pt(111) and highly-corrugated on MgO(100). Theoretical scattering calculations based on the classical trajectory method are used to complement and interpret the experimental data. * Pacific Northwest National Laboratory is operated for the Department of Energy by Battelle under Contract DE-AC06-76RLO 1830.